Image recording apparatus and method

ABSTRACT

Image recording apparatus for recording an image on a recording plate, the apparatus comprising  
     a plate store ( 1 ) for storing a stack ( 12 ) of recording plates separated by interleaved sheets;  
     a drum image scanner ( 6 ) on which recording plates are located for recordal of an image; and  
     a frictional feed apparatus ( 2 ) for withdrawing recording plates from the store ( 1 ) and feeding them singly to the drum image scanner ( 6 ).

FIELD OF THE INVENTION

[0001] This invention relates to a method and apparatus for recording animage on a recording plate.

DESCRIPTION OF THE PRIOR ART

[0002] Lithographic printing plates for which this invention isparticularly well suited typically comprise a rectangular aluminumsubstrate onto which is deposited a thin layer of photographic polymer.In addition a further thin protective coating of a polymer such as PVAis often added.

[0003] Recording of the image information onto such a plate is typicallyachieved in an image scanner using a scanned laser beam which hardensthe photographic polymer in a selective manner. Following recordal ofthe image in the image scanner, the lithographic plate is later usedwithin lithographic printing apparatus. A similar system for therecording of an image may also be used in connection with photographicplates and for the purposes of this invention both lithographic andphotographic plates are described as a recording plate or plates.

[0004] In order to achieve high productivity it is desirable to use animage scanner in conjunction with automatic feeding apparatus tosequentially feed recording plates from a store and deliver them to theimage scanner via a transport system. Typically the store contains astack of such recording plates separated by interleaved sheets whichprotect the sensitive surface of the plates on which the image will berecorded. The delivery of individual plates to the transport system isachieved by removing the top plate from the stack using a feed system.The stack of plates has a typical mass of up to 60 kg, all plates withinthe cassette being of equal size. It is desirable that the apparatus cansupply these plates to the image scanner without manual intervention.Manual intervention is undesirable as it slows the overall processconsiderably and further increases the risk of exposure of the imagerecording surfaces to radiation. For similar reasons it is thereforedesirable that the interleaved sheets are automatically removed from theplate feeding path and are placed in a receptacle for later disposal.These interleaved sheets are often made from paper which is considerablydifferent in mechanical properties when compared with the recordingplates.

[0005] The established practice in existing image processing systems isto withdraw the recording plates sequentially from the stack usingvacuum-activated suckers. The suckers are mounted upon a movable gantryand engage the topmost recording plate, then lifting it clear of thestack. The gantry then moves the recording plate to a receiving positionfor feeding into the image scanner. Separating means are often providedfor the removal of an interleaved sheet when this is the topmostconstituent in the stack. For example such means may include a rollerwhich is moved to engage with the topmost sheet and withdraw it from thestack towards a bin. However, due to adhesion between the topmostrecording plate and one or more plates or interleaved sheets beneath, amultiple feed operation can occur which is required to be remedied byseparation of the plates and sheets. Known methods of performing thisseparation include the blowing of air between the interfaces of theplates and sheets, or simply holding the topmost plate in an elevatedposition above the stack such that the action of gravity eventuallycauses separation of the mis-fed items beneath.

[0006] Typical problems with such a system are that oxygen depletionunder the suckers causes degradation of the emulsion, and secondaryvacuum effects lead to multiple plate feeding.

[0007] One major problem with the use of vacuum suckers is that theyengage in a localized manner with the fragile coated surface of therecording plate. As the vacuum is supplied, the plate deforms locally inthe areas under the suckers producing characteristic circular marks onthe processed plate. A second problem that occurs in such vacuumsystems, is that the vacuum pressure required to lift a plate verticallyis different from that to lift a sheet. If the pressure is not adjustedbetween the feeds then, since the paper is porous, the suckers will liftan interleaved sheet as well as the plate below. The vacuum system musttherefore be capable of distinguishing between plates and sheets and,having set the correct vacuum level and lifted the topmost item, mustconfirm that the separation has been achieved before the selected plateor sheet is moved away from the stack. The time required to performthese steps is relatively large and in many cases rate limiting to theproductivity of the complete system. This method is also unable to beoptimized for a full range of plate sizes and thicknesses. In additionthe apparatus is costly and often unreliable.

[0008] Downstream of the plate store and feeding apparatus conventionalsystems load the recording plate into the drum image scanner and in suchequipment the plate may be supported on an internal or external surfaceof a drum for the recording of an image. Typically the loading of theplate into the image recording position is achieved using rollers ordrive belts. As the exact positioning of the plate is particularlyimportant, such systems include the use of guides and stops to ensurecorrect alignment with the image recording device. De-skewing of theplate is conventionally achieved when the plate is in the imagingposition, by applying of a trail edge force via a sprung system whichapplies a variable force at different points depending on the skewing ofthe plate. However, this relies upon low frictional forces between theplate and the drum, particularly in the case of drums having a smallradius of curvature.

[0009] It is also important to ensure that the surface of the plateconforms with that of the drum, i.e. each part of the plate surface isin contact with the surface of the drum. Prior art systems typicallyachieve this by either using mechanical means to apply a force to theplate causing it to bow and therefore conform with the drum, or byapplying a vacuum to the drum surface causing the plate to be held inthe conforming position. An example of the former method involves theloading of the plate into the apparatus such that the leading edge abutssome end stops. Subsequently, fingers are driven against the rear edgeof the plate causing it to bow outwards and conform with the drum. Asthe apparatus may be used with different sizes of plates, the fingers inthis case may be controlled with stepper motors or a sprung system toensure the correct degree of movement based upon plate size informationgiven to the apparatus controller by an operator.

[0010] In the second case where a vacuum system is used to conform theplate to the drum surface, it is conventional to provide a plurality ofgrooves within the surface of the drum. The grooves are connected toapertures and a vacuum is applied to the grooves using suitable means.The grooves are respectively attached to separate vacuum circuits whichare either switched on or off using a plurality of electronicallycontrolled valves in order to apply a vacuum to an area corresponding tothe size of the recording plate.

SUMMARY OF THE INVENTION

[0011] In accordance with one aspect of the present invention we provideimage recording apparatus for recording an image on a recording plate,the apparatus comprising;

[0012] a plate store for storing a stack of recording plates separatedby interleaved sheets;

[0013] a drum image scanner on which recording plates are located forrecordal of an image; and

[0014] a frictional feed apparatus for withdrawing recording plates fromthe store and feeding them singly to the drum image scanner.

[0015] In accordance with the second aspect of the present invention weprovide a method of feeding recording plates from a plate storecontaining a stack of plates with interleaved sheets, to a drum imagescanner, the method comprising withdrawing plates from the store andfeeding them singly to the drum image scanner all under frictionalcontrol.

[0016] It has been found that frictional feeding apparatus can be usedto successfully withdraw plates from a stack of interleaved plates andsheets in order to feed it to a drum image scanner. It has also beenfound that this feeding operation can be achieved without significantdamage to the sensitive image recording surface.

[0017] In accordance with the third aspect of the present invention weprovide frictional feed apparatus for feeding single recording plates orsingle interleaved sheets from a stack of recording plates andinterleaved sheets, to an output position, the apparatus comprising;

[0018] a nudger member for nudging a plate or sheet in the stack towardsa feed location; and

[0019] a feed member and cooperating separation member at the feedlocation for feeding single plates or sheets to the output position;

[0020] wherein the contact surfaces of the nudger, feed and separationmembers are arranged so as to produce sufficient frictional force whenin contact with either a plate or a sheet, such that plates or sheetsare fed singly towards the output position.

[0021] The feed apparatus described is capable of withdrawing eitherrecording plates or interleaved sheets in a similar manner and passingthem to an output location. The apparatus may be used to withdraw platesor sheets from either the top or the bottom of a stack but preferablythe topmost plates or sheets are withdrawn. The nudger member whichpreferably comprises a nudger roller engages the first plate or sheet inthe stack and passes it to the feed location. Preferably the feed memberis also a feed roller and the sheet or plate is passed into the nip ofthe feed member and the separating member. The nudger and feed membersmay be coupled by suitable means such as a belt, gears or a chain andsprocket. The separating member is preferably a retard pad which maypresent a surface inclined to the feed direction of the plate or sheetto ensure that the nip is maintained but to allow passage of the platesand sheets. The feed and separating members are preferably urgedtogether using urging means. The separating member is preferablypivoted, with an angled pad underneath that is sprung to provide a nipforce. Preferably the urging means comprises a spring attached to theretard pad. The spring therefore provides a force to oppose the movementof the separating member. It will be appreciated that the feed membermay also be movable and provided with urging means.

[0022] In the event of a malfunction during a feed operation, it isdesirable to include means to separate the feed and separating members.This is preferably achieved using a motor and eccentric cam.

[0023] It is desirable that only one member within the frictional feedapparatus drives the plate or sheet forward at any one time andtherefore the apparatus preferably further comprises nudger membermovement means to move the nudger member from the nudging position to aretracted position. This may be achieved using a rotatably mounted cam.In this case the nudger member may simply be returned to the nudgingposition under the action of gravity.

[0024] Preferably the apparatus further comprises stack position sensingmeans to detect when the nudger member is in the nudging position, inorder to feed a plate or sheet from the stack. It will be appreciatedthat the position of the nudger member in contact with the stack neednot be used to measure the position of the next item to be fed from thestack as the position of this item could be measured directly usingappropriate sensing means, for example using an optical sensor.

[0025] Advantageously the use of the feeding apparatus according to thepresent invention greatly improves the speed with which plates can bedrawn from the plate store, for example a feeding speed of 80 mm persecond can be achieved.

[0026] The action of shearing a recording plate from the stack requiresa smaller force than that required to lift the plate vertically and itwill be appreciated that if a vacuum exists between the plate andinterleaved sheets, it is easier to separate these by shearing ratherthan separating them in a direction normal to their contact surface.Typically, the force required to separate a plate by shearing is in therange 1N to 20N, whilst the force required to separate a plate bylifting ranges between 2N and 70N. The magnitude of these forces isaffected by the size of the plates, the environmental conditions, thecondition of the plate stack and storage conditions.

[0027] For example plates stored horizontally at the bottom of a stackof boxes prove very difficult to separate. The use of a smaller force isadvantageous as it reduces the risk of damage to the surface of therecording plates.

[0028] It is also advantageous to use similar apparatus to remove bothrecording plates and interleaved sheets from the stack. Preferably thesethen require selection at a position downstream of the feed location.Typically the selection is achieved by placing a diverter in the path ofthe plate and sheets in order to divert only recording plates in a firstdirection towards the drum image scanner but to divert interleavedsheets in a second direction. Preferably this is achieved using sensingmeans, provided downstream of the feed location, in order to determinethe presence of a plate or a sheet. Preferably the sensing meanscomprises an inductive sensor in order to detect the presence of arecording plate. Similarly an alternative or additional sensing meansmay be provided comprising a first radiation source to illuminate theupper or lower surface of the plate or sheet and a first sensor todetect any reflected radiation at a predetermined location. The materialand surface properties of recording plates and interleaved sheets causeradiation to be reflected in differing ways which allows them to bedistinguished. As a variety of mis-feed scenarios can be envisagedinvolving a combination of plates or sheets, preferably this sensingmeans further comprises a second radiation source and a second sensorpositioned such that the sensing means monitors the reflected radiationfrom both the upper and lower surfaces of the plate or sheet. Thesensing means may then distinguish for example between a singularly fedplate and a plate and sheet fed in combination with the plate topmost ofthe two.

[0029] Preferably the diverter is arranged to be responsive to theoutput of one or more of the sensing means in order to prevent aninterleaved sheet from being mistakenly fed to the drum image scanner.

[0030] As the nudger and feed members contact the sensitive surface ofthe recording plate, it is preferable that they are kept free of debrisand therefore the apparatus preferably further comprises vacuum cleaningmeans to clean the nudger member and/or the feed member. The vacuumcleaning means may also include the use of a brush to dislodge debrisfrom the nudger or feed members. Although the vacuum cleaning means maybe attached to the support member of the nudger or feed members,preferably the vacuum is applied through ducting provided within thesupport member.

[0031] In accordance with a fourth aspect of the present invention weprovide a method of withdrawing recording plates or interleaved sheetsfrom a stack of recording plates and interleaved sheets, the methodcomprising nudging a plate or sheet in the stack towards a feed locationusing a nudger member and feeding the plate or sheet to an outputposition using a feed member with a cooperating separating member at thefeed location wherein the contact surfaces of the nudger, feed andseparation members are arranged so as to produce sufficient frictionalforce when in contact with either a plate or a sheet, such that platesor sheets are fed singly towards an output position.

[0032] Typically the method further comprises moving the nudger memberaway from the nudging position when the first plate or sheet is incontact with the feed or separating members. Preferably the methodfurther comprises the diverting of the interleaved sheets away from theoutput position.

[0033] Once the recording plate has been fed to the output position, itmay then be engaged by an input module. An example of such an inputmodule comprises a friction belt which transports the plate over one ormore rotatably mounted rollers. Preferably, the belt and rollers aredriven at substantially the same velocity. Advantageously the belt androllers are arranged such that only the belt contacts the sensitivesurfaces of the recording plates whereas the opposite surfaces arecontacted with the rollers. Such a cooperating roller and belt systemtransports the plate into the drum of the image scanner.

[0034] Once within the drum, the plate is then engaged with platealignment apparatus which, in accordance with a fifth aspect of thepresent invention, is provided for the alignment of a recording plate ona drum of a drum image scanner, the apparatus comprising; an elongatepusher bar extending along the drum and substantially parallel to thecylindrical axis of the drum, wherein the bar has a pusher surfacehaving an elongate axis extending along the bar and substantiallyparallel with the cylindrical axis, and means for moving the bar in acircumferential manner following the surface of the drum, the elongateaxis of the pushing surface remaining substantially parallel to thecylindrical axis, wherein in use, the pusher surface engages with therearmost edge of a recording plate and urges it to a first position forthe recordal of an image.

[0035] Typically the partial loading of the plate into the drum imagescanner involves passing the plate over the elongate pusher bar of theplate alignment apparatus. The bar may be fitted with additional rollerswhich effectively extend the path of the input module along which theplate is fed. Once the rearmost edge of the plate has passed the pusherbar preferably the pusher bar drops and engages the rearmost edge of theplate. It is preferable that the pusher bar is urged against the surfaceof the drum to ensure that it correctly engages with the plate's rearedge.

[0036] The movement of the bar may be achieved using pinions mounted tothe pusher bar and corresponding tracks mounted upon the drum, the barbeing fixed to the drum using suitable bearings mounted on a rimprovided at the drum edges.

[0037] It is envisaged that the alignment means according to the presentinvention may be used together with vacuum conforming means to conformthe plate. Alternatively it may be used to apply the required bendingforce to the plate as part of a mechanical conforming means.

[0038] The circumferential motion of the pusher bar drives the platefrom the rear towards a punching means which preferably comprisesretractable end stop pins against which the plate is urged. Theretractable end stops are positioned within the drum to abut the leadingedge of the recording plate when the plate is located in the firstposition. Typically at least one sensor is positioned to detect theleading edge of the plate when it approaches the pins.

[0039] Preferably lateral correction means are also fitted to thepunching means to correct the position of the plate in a directionsubstantially parallel to the cylindrical axes of the drum. Such meansmay comprise pins which are symmetrically opposed about the centre ofthe drum's cylindrical axis. The pins in this case therefore remainequidistant from the centre of the drum and are moved inwards in orderto engage with the sides of the plate causing it to be positionedcentrally.

[0040] Preferably the apparatus further comprises a slip clutch mountedto the moving means of the pusher bar. This allows the bar to be pushedagainst the rearmost edge of the plate after lateral positioncorrection, to effect the final plate positioning in the apparatus, theforce with which the plate is urged against the end stop pins beingdetermined by the slip clutch.

[0041] Advantageously the punching means is arranged to remove at leastone portion of the recording plate. This may be achieved preferablyusing at least one punch indenter which passes through the plate duringpunching and holds the plate in position during later imaging.

[0042] Having positioned the plate within the apparatus it isadvantageous to conform the plate to the surface of the drum usingvacuum means.

[0043] In accordance with a sixth aspect of the present invention weprovide a drum of a drum image scanner for locating recording plates ofdiffering dimensions on the surface of the drum, the surface of the drumon which the plates are located containing a plurality ofcircumferentially extending axially spaced grooves, wherein each groovecontains at least one aperture, all the apertures being connected to avacuum source whereby all the apertures receive substantially the samevacuum level at all times, the apertures being located such that, whenat least part of the length of a groove is covered by a plate, thecovered portion contains the aperture or apertures opening into thatgroove.

[0044] This arrangement is advantageous in that complex and expensivevalve mechanisms are not required for the performance of the invention.Typically each groove is closed at one end such that it does not extendto the edge of the drum, and contains only a single aperture.Advantageously this arrangement of grooves and apertures in connectionwith a vacuum source provides the capability of conforming various sizesof recording plates to the surface of the drum without the need forcomplicated vacuum circuits.

BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Examples of the image recording apparatus and method according tothe present invention will now be described in accordance with theaccompanying figures in which;

[0046]FIG. 1 is a simplified side view of the image recording apparatus;

[0047]FIG. 2 is a side view of the plate feeding apparatus;

[0048]FIG. 3 is a side view of the input module;

[0049]FIG. 4 is a perspective view of the input modules;

[0050]FIG. 5 is a perspective view of the plate alignment apparatus;

[0051]FIG. 6A is a perspective view of the drum containing grooves; and

[0052]FIG. 6B illustrates the view along one groove.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0053] An example of the apparatus according to the present invention isshown in FIG. 1.

[0054] The apparatus comprises a plate store 1 which contains a stack ofradiation-sensitive lithographic recording plates. A variety of platesizes may be used, typical dimensions lying within the range 400-960 mmlength (front to rear edge) and 500-1160 mm in width. These plates areseparated by interleaved sheets of paper. The topmost item (either aplate or sheet) in the stack is fed from the stack by frictional feedapparatus indicated generally at 2. The item is first sheared from theitems below by a nudger member and is then passed to a feed member.

[0055] As the topmost item may not always be sheared from the itembeneath, for example a sheet may stick to the underside of a plate, thefeed member cooperates with a separating member to separate the topmostitem from any additional items adhered to it. The initial shearing ofthe item from the stack and the separation of any adhered items isachieved using frictional forces applied to the surfaces of the items.

[0056] When the topmost item has been successfully separated it isidentified using sensing means and passed to a diverter 3 The diverterdirects single recording plates in a first direction towards a pluralityof axially spaced input modules generally indicated at 4. Interleavedsheets or any combination of recording plates and interleaved sheetsidentified by the sensing means as being mis-fed are diverted by adiverter 3 in a second direction towards a receptacle 5.

[0057] Each input module comprises a transport path formed between aband held against a train of rollers, receives a recording plate andpasses it along an arced path onto the inner drum surface of a drumimage scanner 6.

[0058] The rear edge of the recording plate is then engaged by a pusherbar 7. The pusher bar transports the plate over the internal surface ofthe drum to a recording position where it is conformed with the internalsurface of the drum using vacuum means 8.

[0059] Following the recordal of an image on the recording platesurface, the pusher bar 7 is used to move the plate towards an exitposition where it is removed from the drum using an output module,generally indicated at 9.

[0060] In order to automate the process, an electronic system controller200 shown in FIG. 1, is provided to operate the apparatus usinginformation inputted by a human operator and additional signals providedby sensing means positioned within the apparatus.

[0061] Each aspect of the apparatus will now be described in moredetail.

[0062] The frictional feed apparatus is shown in more detail in FIG. 2.

[0063] The plate store 1 comprises a light sealed cassette 10 containinga platen 11 upon which a stack 12 of recording plates is placed.Conventionally as in this example, the plates are separated byinterleaved sheets of paper. The cassette has a lid 13 ensuring that thecassette is light-sealed when not in use. The front end of the cassetteis defined as the end which is inserted into the feed apparatus and fromwhich the plates are withdrawn.

[0064] The front part of the lid 13 comprises a hinged section 14allowing the front section 14 to be raised with respect to the rest ofthe lid 13. Means are provided within the apparatus to open the lid asthe cassette is inserted. A stack increment member 15 forming part ofthe feeding apparatus is arranged to contact platen 11 on its undersidenear to the front end of the cassette, the increment member 15 passingthrough the base of the cassette. The increment member allows the frontend of the platen 11 to be lifted from beneath which in turn lifts thefront end of the stack. The lifting of the stack raises part of thestack above the front wall of the cassette. An alternative arrangementcan also be envisaged in which the whole stack is raised whilstremaining substantially horizontal. The stack increment 15 is engaged bya increment mechanism 16 which in turn is driven by an increment motor17 in response to the system controller 200.

[0065] Upper and lower elevator shelves 18 are provided as part of theapparatus housing and the cassette is loaded between these in a slidablemanner. The sliding of the cassette into the apparatus is aided byroller ball units 19 attached to the base of the cassette.

[0066] A lead edge guide 20 is provided as part of the feed apparatus,the guide 20 being positioned so as to act as a wall and allow only thetopmost items to be removed from the stack by the feed apparatus. In thepresent example, the underside of the topmost item in the stack istypically only 0.3 mm above the top surface of the lead edge guide 20. Anudger roller 21 mounted upon an axle 22 is positioned above the topmostitem at the front end of the stack. The nudger roller is mounted suchthat it can be lowered to contact the upper surface of the topmost item.Similarly a feed roller 23, of similar dimensions to the nudger roller21, is mounted on an axle 24 in a position substantially parallel withthe axis of the roller 21 but in a position downstream of the nudgerroller, both axles being mounted in a support 25. The rollers 21 and 23are coupled by a drive belt 26 entrained about a drive pulley wheelattached to each axle. An additional drive pulley wheel 27 is attachedto the feed roller axle 24. The pulley wheel 27 is provided with aone-way clutch which allows driving of the feed roller only in the feeddirection (anticlockwise in FIG. 2).

[0067] About this pulley wheel 27 is entrained a second drive belt 28which provides drive to the feed roller from a drive motor 29. Thepulley wheels are arranged such that when the motor 29 is driven in afeed direction, drive is transmitted to both the nudger and feed rollersto drive an item towards the drum image scanner. On the other hand ifthe drive direction of the motor is reversed, the one-way clutch ensuresthat no power is provided to the feed roller but that the nudger rolleris driven in the opposite direction and allows plates or sheets to bepassed back into the cassette. This is particularly advantageous in theevent of a mis-feed malfunction. It will be appreciated that chains andsprockets could be used as an alternative method of driving the rollers.

[0068] A lifting member 30 is attached to the support 25, the supportbeing pivoted about the position of the feed roller axle 24. A lift cam31 driven by a lifting motor 32 is arranged to engage with the liftingmember to raise the free end of the support by pivoting it about theaxle 24. The nudger roller can therefore be moved between a firstposition where it is in contact with the topmost item, to a liftedposition where no contact occurs. In order to increase the frictionalforce and feed efficiency, an additional mass (not shown) may be addedto the support 25. Stack position sensing means X (shown in FIG. 2) arealso provided, attached to the housing of the frictional feed apparatus.When the top of the stack is in the correct position for the feeding ofthe topmost item, the nudger roller contacting the stack will be locatedat a certain position with respect to the feed roller about which it ispivoted. The stack position sensing means X detects when the support 25is angled at the correct position with respect to the pivot, and asignal is sent to the system controller 200.

[0069] The frictional feeding apparatus also contains vacuum cleaningmeans comprising tubes 33,34 running along the length of the nudger andfeed rollers respectively. Elongate apertures 35 and 36 are provided inthe tubes along a direction substantially parallel with the axis of therollers, and at a position adjacent the roller surfaces. The tubes areconnected to vacuum supply means which draws air over the surface of therollers through the slots 35 and 36 and along the tubes 33 and 34towards the vacuum source. Brushes 37 and 38 are additionally provided,running along the lengths of the nudger and feed rollers to dislodge anydebris which will be removed by the vacuum means.

[0070] A retard pad 39 is positioned beneath the feed roller 23. In thisexample the retard pad is 10 mm longer than the feed roller to preventcreasing of the recording plates. The retard pad is urged into contactwith the feed roller using two axially spaced springs 40. The pad ispivoted about an axis parallel with that of the feed roller, the axisbeing positioned at the upstream end of the pad. The retard pad isarranged such that it is angled in an upward direction towards the feedroller and is forced against the feed roller with the spring 40. The padis arranged so that the nip between the pad and the roller is notpositioned at the downstream end of the pad but rather away from the endby a small distance to increase its effectiveness. The pad thereforepresents an upwardly inclined surface to an item being fed. The pad isalso positioned such that the leading edge of an item being fed towardsthe nip contacts the surface of the pad a small distance upstream of thenip, and is deflected slightly upwards before entering the nip. Thisaids the separation of any multiply fed items as they are encouraged tobe sheared prior to entering the nip.

[0071] A retraction member 41 is attached in a position near to theupper end of the pad beneath the feed roller. In the event of theapparatus jamming the pad can be retracted by the rotation of a drivencam 42 which engages with the retraction member 41. This pivots the padaway from the feed roller.

[0072] A nip sensor 50 is positioned downstream of the feed roller andadjacent the nip. The sensor is formed from a simple light source anddiode which detects the presence of a plate or sheet by the action ofobscuring the light from the source. The signal from the sensor 50 ismonitored by the system controller 200. Sensing means 45 and 46 couldalternatively be used to detect the presence of an item in the nip ifthey were correctly located adjacent the nip.

[0073] A plate guide 43 is provided downstream of the feed apparatus tosupport plates and interleaved sheets being fed from the feed roller. Adiverter 3 is provided downstream of the plate guide 43, the diverterbeing deflected by a solenoid between a first position and a secondposition. Alternatively a motor driven system could be used.

[0074] At a position between the nip and the diverter 3, an inductivesensor 44 is located to detect the presence of a metallic recordingplate. This information is used by the system controller 200 to identifythe item and to position the diverter 3 in a first position in the caseof a plate being detected, and a default second position in the casethat a plate is not detected. Plates identified using inductive sensingare fed in the first direction along a second guide 47 towards furthersensing means 45,46 and the image scanner; whereas interleaved sheetsare fed in a second direction into the nip of driven rollers 48 and 49.These rollers are constructed from a resilient material. They arearranged so as to provide a strong nip force capable of removing anyitem from the system which is placed in the nip between them. Theserollers are then driven to forcibly remove the sheets from the feed pathfor disposal into the container 5.

[0075] Further downstream of the diverter, sensing means 45 and 46 arepositioned above and below the path of the fed items respectively. Eachsensing means comprises a radiation emitter and a reflected radiationreceiver although alternative means capable of distinguishing betweenplates and sheets could be used. In this example a light source is usedin each case in conjunction with a corresponding photodiode to detectthe intensity of the light reflected from the upper and lower sides ofthe fed item.

[0076] One critical parameter is the difference between the coefficientsof friction of the feed roller and the retard pad. It is suggested thatthis is greater than the coefficient of friction between either surfaceof a recording plate and an interleaf sheet. The results of measurementsof the coefficient of friction, μ, between relevant surfaces are shownin Table 1 below. TABLE 1 Materials μ (Typical) Rollers: Polyisoprene onEmulsion 2.3 Retard Pad: Microcellular Urethane 150 on Plate 1.2 Betweenfed items: Aluminium side of plate on Interleaf 0.5 Emulsion side ofplate on interleaf 0.3

[0077] It has been found that polyurethane materials are suitable forthe construction of the feed and nudger rollers, isoprenes being used inthis particular example. Similar materials may be used as the contactsurface for the retard pad and for the rollers 48 and 49.

[0078] In this example the friction feed apparatus is centrally locatedwith respect to a point halfway along the cylindrical axis of the drumimage scanner. The rollers and retard pad are considerably narrower inwidth than the drum although a system in which they were the same widthcould be used.

[0079] The operation of feeding individual plates or sheets from thestack will now be described. A stack of recording plates separated byinterleaved sheets is provided within the light seal cassette 10. Thecassette is slidably inserted within the apparatus assisted by theroller ball units 19 running along the lower elevator shelf 18. As thecassette is inserted towards its loaded position, guides are used toraise the hinged portion 14 of the lid. When the cassette is correctlyloaded, the lift motor 32 is operated causing the cam 31 to rotate andthe nudger roller is lowered onto the topmost plate or sheet by theaction of the gravity. The front end of the platen is then lifted by theaction of the plate stack increment mechanism 16 being driven by theincrement motor 17. The lifting of the platen at the front end raisesthe topmost plates and sheets clear of the front lip of the cassette.When the topmost items clear the top of the lead edge guide above, theposition of the nudger roller causes the stack position sensing means Xto send a signal to the system controller 200 and the increment motor ishalted. When the cassette is correctly loaded, the lead edge guide 20acts as a surface against which all but the very topmost plates in thestack abut. This guide therefore prevents a large number of plates andsheets being fed towards the feed roller. The drive motor 29 is thenactivated which rotates both the feed and nudger rollers. The frictionforce, normal force and roller torque between the nudger roller and thetopmost item in the stack causes the item to be sheared from the rest ofthe stack and driven towards the nip of the feed roller and retard pad.During correct operation when a single plate or sheet passes between thefeed roller 23 and the retard pad 39, the action of the feed roller 23is sufficient to drive the plate or sheet onto the plate guide 43against the resistance of the retard pad. However, it is undesirable todrive the plate or sheet with both the nudger and feed rollers as minorspeed differentials result in scrubbing or buckling and therefore thenip sensor 50 is used to detect the presence of a plate or sheet withinthe nip. A signal from the sensor 50 is sent to the system controller200 and this then operates the motor 32 to rotate the cam 31. Therotation of the cam has the effect of lifting the nudger roller from thesurface of the plate or sheet but because the support 25 is pivotedabout the axle 24, the feed roller 23 remains in contact with the feditem.

[0080] Although the presence of the lead edge guide 20 should prevent alarge scale mis-feed, it is possible for a small number of plates andsheets to be fed in a group towards the nip of the feed roller andretard pad. Usually, the angle and position of the retard pad 39 withrespect to the feed roller 23 provides a sufficient shearing force toseparate the topmost item from any others attached to it beneath,particularly as the leading edge contacts with the retard pad firstbefore entering the nip. However, in the case of a multiple feed thespring 40 allows the retard pad to deflect and the multiple items aredrawn into the nip.

[0081] As the position of contact between the feed roller and the retardpad occurs at a distance away frog the end of the retard pad, andbecause the retard pad is angled in an upward direction, any multiplyfed items experience a greater shearing force as they pass further intothe nip. This enhances the possibility that they may be separated.

[0082] In the unlikely event of a large number of adhered plates andsheets are passed into the nip causing a jam of the system, the motor 29can be stopped. The retard pad can be lowered by the action of the cam42 engaging with the retraction member 41 and the items can be returnedto the cassette by the later reversal of the motor 29. Due to the actionof one-way clutch attached to the feed roller, only the nudger roller isdriven in the reverse direction which allows the mis-fed items to beremoved. As the cassette is light sealed, the items can be replacedwithin the cassette and the cassette replaced. Conveniently thereplacing of the items within the cassette prevents exposure of therecording plates to light.

[0083] It is important that only recording plates are fed to the drumimage scanner and that there is no possibility of feeding anything butsingle recording plates. During normal operation, the presence of aplate is detected by the inductive sensor 44 and the diverter 3 ispositioned to pass the plate towards the image scanner. At all othertimes when a plate is not present the diverter is positioned to directany items towards the container 5 via the driven rollers 48,49. However,to deal with the slight possibility that a plate and sheet may passthrough the nip, the plate being detected by the sensor 44 and passedtowards the image scanner onto the plate guide 47, the sensing means 45and 46 are positioned downstream of the diverter 3. The fed item isidentified due to the differences in reflectivity between interleavedsheets and either surface of a recording plate. If the controller 200identifies signals from both sensing means 45 and 46 that correspond toa recording plate then the system controller 200 allows the plate tocontinue downstream and to be loaded into the drum image scanner. Ifthis is not the case, for example if signals are detected correspondingto a plate on one side and a sheet on another, then the controller 200halts the system allowing the mis-feed operation to be corrected.

[0084] A successfully identified and separated recording plate being fedalong the second plate guide 47 is then engaged by the input moduleapparatus in order to load the plate into the drum image scanner. Theposition of the input module 4 with respect to the drum of the imagescanner is shown in FIG. 3.

[0085] The input module apparatus 4 comprises a plurality of idlerrollers 65 which are rotatably mounted upon axles 66 held within asupport 67. The idle rollers 65 are arranged in an arc to divert theplate from the feed direction in a curved path into the drum 80 of thedrum image scanner 6. In the present example, the radius of curvature ofthe arc is not less than 200 mm at any point and the path of the plateis diverted through 115 degrees into the drum.

[0086] Driven soft rubberized rollers 68 are provided at positions bothupstream and downstream of the curved path of the idler rollers andprovide a smooth extension to the curved train of idler rollers 65. Inorder to hold the recording plate in contact with the driven and idlerrollers, a driven band 69 is provided which is entrained about threecrown rollers 71,72,73. Crown roller 71 is positioned upstream of theupstream driven roller 68 but is positioned on the opposite side of therecording plate feed path. Similarly crown roller 72 is provided in aposition downstream of the downstream driven roller 68 and again ispositioned on the opposite side of the recording plate path. The band 69supports the upper surface of the plate as it is transported through thefeed path, the underside being supported by the train of rollers. Thepressure applied by the band to the emulsion surface of the plate neverexceeds 1N/mm².

[0087] The third crown roller 73 is positioned so as to ensure that theparts of the band 69 not forming part of the curved path, are kept clearof the driven and idler rollers and provide a pre-determined tension.One-way clutches are used on all of the driven rollers to aid theclearance of any plates jammed in the apparatus. The rollers are alsoprovided with knobs so that they can be rotated manually.

[0088] Cleaning strips 74 are also provided to remove debris from theband and are conveniently located at a position contacting the band 69where the band is not in use as part of the curved feed path. The driverollers 68 and crown rollers 71 to 73 are driven by a single motor toensure that both sides of the feed path are driven at a similarvelocity. Rubber materials are suitable for use as the contact surfacesof the rollers. The apparatus is capable of transporting the plates atspeeds of up to 250 mm per second if required.

[0089] Due to the dimensions of the recording plate, a plurality ofinput modules of the form described are provided in parallel along thedirection of the cylindrical axis of the drum image scanner. This ismore clearly shown in FIG. 4 in which a plurality of input modules 4 areshown. It will be noted that the input modules 4 are not equally spacedalong the cylindrical axis of the scanner but are symmetrically arrangedabout the point half way along the drum. The positioning of the inputmodules is determined by the various widths of recording plates used inthe industry.

[0090] The alignment of the centre of the feeding apparatus with thecentre of the drum image scanner conveniently allows plates of variouswidths to be used.

[0091] Returning to FIG. 3, during operation, the leading edge of arecording plate is passed into the input module at a position 60. Theleading edge of the plate is then engaged in the nip between theupstream driven roller 68 and the band 69. The plate is then fed by thedriving action of the rollers and band along the curved path of theroller train, the band ensuring that the plate is held against theserollers as it is transported through the arc. The front edge of theplate is then engaged by the downstream driven roller 68 and is driveninto the drum 80 of the drum image scanner. As the plate enters the drumit passes over an idler roller 95 attached to the plate alignmentapparatus 82, which will now be described.

[0092] The alignment means 82 is shown in FIG. 5. The alignment meanscomprises a support shaft 90 at one end of which is positioned a firstend support 91, and at the other end a second end support 92. Parallelto the support shaft and in an adjacent position is mounted a driveshaft 93 which is rotatably mounted on an axle into the end supports 91and 92. The drive shaft 93 is supported at a plurality of positionsalong its length by shaft supports 94. Upon some of the shaft supports94 are mounted sprung idler rollers 95 and each of the supportscontaining the idler rollers are positioned such that they align alongthe cylindrical axis of the drum with the positions of the input modules4. When the alignment means 82 is in its start position during theloading of the recording plate into the drum, the idler rollers 95engage with the band 69 and form a continuation of the curved path (seeFIG. 3). This assists with the loading of the recording plate into thedrum 80.

[0093] Referring to FIG. 5, on the opposite side of the parallel shaftsfrom the idler rollers 95, an elongate pusher bar 96 is located. Thisbar is attached to the supports 94. Pinions 97 are non-rotatably mountedonto the drive shaft 93 at a position adjacent the end supports 91, 92.These pinions 97 run in corresponding tracks 98 attached to each end ofthe drum 80. The tracks 98 are arranged to conform with the internalsurface of the drum 80, such that the movement of the alignment meansalong the tracks 98 causes the pusher bar 96 to pass across the internalsurface of the drum. As the internal surface of the drum is formed in acylindrical manner, the orientation of the bar with respect to the drumsurface is maintained by bearings positioned at each end of thealignment means 82. In order to attach the alignment means to thesurface of the drum, a lip is provided around the circumference of thedrum 80 at each edge. Eccentric bearings and pitch rings are used toensure that the alignment means remains in the correct orientation andgeared within the tracks at all times.

[0094] The pusher bar 96 is constructed from polycarbonate and is biasedagainst the surface of the drum, causing constant contact with the drumat all points along the bar. This biasing ensures that the edge of theplate does not pass between the bar and the drum surface. The movementof the alignment means is powered by a motor (not shown) coupled to thedrive shaft 93. A slip clutch is provided as a coupling between themotor and the drive shaft which prevents movement of the alignment meansif it encounters sufficient resistance.

[0095] Sensing means 99 are provided in a position adjacent the idlerrollers 95 to detect the passage of the trailing edge of the recordingplate.

[0096] Once the trailing edge has passed the sensing means 99, thecontroller 200 operates the alignment means 82. The drive shaft 93 isrotated and this causes the alignment means 82 to move in a directionfollowing the surface of the drum whilst the long axis of the alignmentmeans remains parallel with the central cylindrical axis of the drum 80.The orientation of the pusher bar 96 with respect to the drum surface isconstantly maintained during the movement of the alignment means.

[0097] The motion of the alignment means 82 causes the rear edge of therecording plate to be engaged by the pusher bar 96. The bar transportsthe plate towards an imaging position and due to the parallel nature ofthe bar with the cylindrical axis, the driving of the plate only bycontact with the rear edge ensures that the rear edge of the plate isparallel with the cylindrical axis and is therefore deskewed by the timeit arrives at the imagine position.

[0098] The plate is driven around the surface of the drum until thefront edge enters a punching means 120. The punching means contains fourretractable pins 111 which act as front stops for the plate and againstwhich the plate abuts when correctly located for imaging. For wideplates the leading edge abuts all four pins, smaller plates onlycontacting with the two centremost pins. As shown in FIG. 3, a sensor100 detects the arrival of the front edge of the recording plate in thepunching means.

[0099] One or more punching indenters 112 are provided within thepunching means to remove through thickness sections of the recordingplate for the purpose of accurate alignment of the plate within theprinting apparatus downstream of the scanner. The apparatus may beprovided with the ability to punch a variety of different shapes out ofthe plate in accordance with the various printing presses used in theindustry. The punching means in the present example has the capabilityof punching up to 13 slots or holes along the edge of a plate, alongwith two different punch options for different types of printing press.

[0100] Centring means are also provided as part of the punching means,the centring means comprising two movable pins. The pins are mountedusing rack and pinion apparatus and are arranged to move incorrespondence with each other such that at all times, each pin isequidistant from a point halfway along the cylindrical axis of thescanner. The pins are arranged to move only in a direction parallel withthe cylindrical axis and this is achieved using a rack for each pin anda single pinion. The use of the pusher bar advantageously ensures thatthe plate is not substantially skewed by the action of the centringmeans.

[0101] The retractable pins 111, punch indenters 112 and the centringmeans are controlled by the system controller 200.

[0102] When the front edge of the recording plate is detected by thesensor 100, the movement of the alignment means is halted. However, dueto the time delay required to achieve this, the sensor 100 is notpositioned such that the front edge of the plate abuts the end stopswithin the punch. Once the movement of the recording plate has halted,the centring pins are brought in from either side of the plate by thecontroller 200 to centre it laterally within the drum. The pusher bar isthen driven forwards again and the plate is pushed against theretractable pins 111 within the punch. This causes sufficient resistanceagainst the bar for the slip clutch to slip which is detected by thecontroller 200 using a sensor. The controller 200 accordingly stops themotion of the bar and the front end of the recording plate is thenpunched by the punching indenters 112. This method can be used toreproducibly register the plates within a 200 micrometer repeatabilityskew range. Unlike conventional punching means, the punch has a bridgedform which allows the passage of the whole plate through the punchrather than requiring the plate to be withdrawn in a reverse directionfollowing punching.

[0103] Once the indenters have passed through the plate they are held inposition to further secure the plate whilst the controller 200 thenapplies the vacuum means to conform the plate fully to the surface ofthe drum for imaging.

[0104] As shown in FIG. 6A the vacuum means comprises a series ofparallel grooves 120 positioned within the internal surface of the drum.A plurality of grooves (22 in the present example) are provided andthese are not equally spaced axially along the drum but rather arepositioned according to the various sizes of plate which will be usedwithin the scanner. Each groove does not fully extend around the drum,the downstream end of each groove being closed at a positioncorresponding to the location of the front edge of the plate duringimaging. At 350 mm from the closed end of each groove, a circularaperture 102 is provided in the groove base, this distance being smallerthan the 400 mm length of the smallest plate type used in the apparatus.

[0105] In each case the rest of the groove continues around the internalsurface, at a constant distance along the cylindrical axis, andterminates at the edge of the drum at the upstream side. Vacuum supplytubes 103 are connected to each aperture as shown in FIG. 6A and theseare collectively connected to a main vacuum tube 104 via a manifold 105.This ensures that each aperture experiences a similar vacuum level atall times. In this case the grooves are of square cross-section with theside of the square being 1 mm in length and the aperture is circularwith a 1 mm diameter (see FIG. 6B).

[0106] When the recording plate is correctly positioned within theapparatus and the punching indenter is engaged, the controller 200applies the vacuum to the grooves in order to conform the plate to thesurface of the drum. The positioning of the aperture within each grooveensures that if a groove is partially covered by a plate, then therespective aperture is also covered whereas those grooves which are notcovered do not sufficiently reduce the efficiency of the vacuum source.

[0107] Using this method of conforming the plates, the underside of therecording plates can be brought within 50 micrometers of the drumsurface at all points.

[0108] When the recording plate is held in position by the vacuum, thecontroller 200 initiates an imaging step after which the vacuum isreleased, the indenter pins 112 are removed and the front stop pins 111are retracted.

[0109] The alignment means is then used to push the recording plate fromthe imaging position further towards an output position. At the outputposition a guide 110 guides the front edge of the recording plate intothe nip formed by a band and driven roller of the output modules. Theoutput modules 9 are of similar form to the input modules although ofslightly different geometry. Again the output modules comprise bands androllers in order to pass the recording plate though a curve and ontowards apparatus downstream of the drum image scanner. The pusher baris then returned to its first position in order to receive the nextplate for imaging, the time taken between unloading of(an exposed plateand the loading of the next one being less than 30 seconds.

We claim:
 1. Image recording apparatus for recording an image on arecording plate, the apparatus comprising: a plate store for storing astack of recording plates separated by interleaved sheets; a drum imagescanner on which recording plates are located for recordal of an image;and a frictional feed apparatus for withdrawing recording plates fromthe store and feeding them singly to the drum image scanner.
 2. A methodof feeding recording plates from a plate store containing a stack ofplates with interleaved sheets, to a drum image scanner, the methodcomprising withdrawing plates from the store and feeding them singly tothe drum image scanner all under frictional control.
 3. Frictional feedapparatus for feeding single recording plates or single interleavedsheets from a stack of recording plates and interleaved sheets, to anoutput position, the apparatus comprising: a nudger member for nudging aplate or sheet in the stack towards a feed location; and a feed memberand cooperating separation member at the feed location for feedingsingle plates or sheets to the output position; wherein the contactsurfaces of the nudger, feed and separation members are arranged so asto produce sufficient frictional force when in contact with either aplate or a sheet, such that plates or sheets are fed singly towards theoutput position.
 4. Apparatus according to claim 3, wherein the nudgermember is a nudger roller.
 5. Apparatus according to claim 3, whereinthe feed member is a feed roller.
 6. Apparatus according to claim 3,further comprising nudger member movement means to move the nudgermember from the nudging position to a retracted position.
 7. Apparatusaccording to claim 6, wherein the nudger member movement means comprisesa rotatably mounted cam.
 8. Apparatus according to claim 6, furthercomprising stack position sensing means to detect when the nudger memberis in the nudging position.
 9. Apparatus according to claim 3, furthercomprising a motor to move the separating member.
 10. Apparatusaccording to claim 3, wherein the separating member further comprises aspring to provide a force to oppose the movement of the separatingmember.
 11. Apparatus according to claim 3, wherein the separatingmember is a retard pad.
 12. Apparatus according to claim 11, wherein theretard pad presents a surface inclined to the feed direction of a plateor sheet.
 13. Apparatus according to claim 3, further comprising sensingmeans positioned downstream of the feed location for detecting if asingle plate has been successfully fed.
 14. Apparatus according to claim13, wherein the sensing means is an inductive sensor.
 15. Apparatusaccording to claim 13, wherein the sensing means illuminates the surfaceof the plate or sheet with radiation and monitors the reflectedradiation.
 16. Apparatus according to claim 13, further comprising asheet diverter positioned downstream of the feed location, wherein thesheet diverter is responsive to the sensing means and diverts plates ina first direction and sheets in a second direction.
 17. Apparatusaccording to claim 16, further comprising second sensing meanspositioned downstream of the sheet diverter in the first direction fordetecting if only a single plate has been diverted in the firstdirection.
 18. Apparatus according to claim 17 wherein the secondsensing means comprises a first radiation source to illuminate the uppersurface of the plate or sheet and a first sensor to monitor thereflected radiation, and a corresponding second radiation source and asecond sensor positioned to monitor radiation reflected from the lowersurface of the plate or sheet.
 19. Apparatus according to claim 3,further comprising vacuum cleaning means to clean the nudger memberand/or the feed member.
 20. Apparatus according to claim 19 wherein thevacuum is applied through ducts positioned within the support of thenudger member or the feed member.
 21. Apparatus according to claim 19,further comprising a brush attached to the nudger member or the feedmember in order to dislodge debris.
 22. A method of withdrawingrecording plates or interleaved sheets from a stack of recording platesand interleaved sheets, the method comprising nudging a plate or sheetin the stack towards a feed location using a nudger member and feedingthe plate or sheet to an output position using a feed member with acooperating separating member at the feed location wherein the contactsurfaces of the nudger, feed and separation members are arranged so asto produce sufficient frictional force when in contact with either aplate or a sheet, such that plates or sheets are fed singly towards anoutput position.
 23. A method according to claim 22, wherein the methodfurther comprises moving the nudger member away from the nudgingposition to a retracted position when the plate or sheet is in contactwith the feed or separating members.
 24. A method according to claim 22,further comprising diverting the plates in a first direction and theinterleaved sheets in a second direction.
 25. Plate alignment apparatusfor the alignment of a recording plate on a drum of a drum imagescanner, the apparatus comprising: an elongate pusher bar extendingalong the drum and substantially parallel to the cylindrical axis of thedrum, wherein the bar has a pusher surface having an elongate axisextending along the bar and substantially parallel with the cylindricalaxis, and means for moving the bar in a circumferential manner followingthe surface of the drum, the elongate axis of the pushing surfaceremaining substantially parallel to the cylindrical axis, wherein inuse, the pusher surface engages with the rearmost edge of a recordingplate and urges it to a first position for the recordal of an image. 26.Apparatus according to claim 25, wherein the moving means is adapted tomove the bar so as to move the plate from its first position towards adrum exit position.
 27. Apparatus according to claim 25, furthercomprising lateral correction means for correcting the position of aplate in a direction substantially parallel to the cylindrical axis ofthe drum.
 28. Apparatus according to claim 25, further comprisingpunching means to remove at least one through thickness portion of therecording plate.
 29. Apparatus according to claim 28, wherein thepunching means comprises a punch indenter which passes through the plateduring punching.
 30. Apparatus according to claim 25, wherein the movingmeans comprises pinions mounted to the pusher bar and correspondingtracks mounted upon the drum.
 31. Apparatus according to claim 25,further comprising retractable end stops positioned within the drum toabut the leading edge of the recording plate when the plate is locatedin the first position.
 32. A drum of a drum image scanner for locatingrecording plates of differing dimensions on the surface of the drum, thesurface of the drum on which the plates are located containing aplurality of circumferentially extending axially spaced grooves, whereineach groove contains at least one aperture, all the apertures beingconnected to a vacuum source whereby all the apertures receivesubstantially the same vacuum level at all times, the apertures beinglocated such that, when at least part of the length of a groove iscovered by a plate, the covered portion contains the aperture orapertures opening into that groove.
 33. Apparatus according to claim 32,wherein each groove is closed at one end.
 34. Apparatus according toclaim 32, wherein each groove contains a single aperture.